This invention relates to disposing metal contaminated material containing soluble vanadium as landfill. Examples of such vanadium contaminated materials are spent cracking catalysts and spent contact material used in a selective vaporization process for upgrading heavy petroleum crudes, resid fractions of petroleum crudes or the like.
The Asphalt Residual Treating (ART.SM.) Process is a decarbonizing and demetallization process that has been developed to treat residual stocks and heavy crudes for the removal of contaminants. The process is described in numerous publications, including "The ART Process Offers Increased Refinery Flexibility", R. P. Haseltine et al, presented at the 1983 NPRA Conference in San Francisco. See also U.S. Pat. No. 4,263,128 to Bartholic. The process is a non-catalytic technological innovation in contaminant removal and will typically remove over 95% of the metals, essentially all the asphaltenes and 30% to 50% of the sulfur and nitrogen from residual oil while preserving the hydrogen content of the feedstock. The process enables the subsequent conversion step in residual oil processing to be accomplished in conventional downstream catalytic processing units.
The ART Process utilizes a fluidizable solid particulate contact material which selectively vaporizes the valuable, lower molecular weight and high hydrogen content components of the feed. The contact material is substantially catalytically inert and little if any catalytic cracking occurs when the process is carried out under selected conditions of temperature, time and partial pressure. Generally, suitable contact material has a relatively low surface area, e.g., 5 to 20 m.sup.2 /g as measured by the BET method using nitrogen. Presently preferred contact materials are silica-aluminas produced by calcining microspheres containing kaolin clay. Heavy metals are deposited on the contact material and removed. High molecular weight asphaltenes also deposit on the contact material, some asphaltenes being converted to lighter product. Because the contact material is essentilly catalytically inert, very little molecular conversion of the light gas oil and lighter fractions takes place. Therefore the hydrogen content of these streams is preserved. In other words, the lighter compounds are selectively vaporized. It is believed that the molecular conversion which does take place is due to the disproportionation of the heavier, thermo-unstable compounds present in the residual feedstock.
The hydrogen content of the coke deposited on the contact material is typically less than four percent. Coke production is optimally equivalent to 80% of the feedstock Conradson Carbon Residue content. Heat from the combustion of coke is used internally within the ART system. Surplus heat may be recovered as steam or electric power. No coke product is produced.
The ART Process is adapted to be carried out in a continuous heat-balanced manner in a unit consisting primarily of a contactor, a burner and an inventory of recirculating contact material. Chargestock is contacted with particles of hot fluidizable contact material for a short residence time in the contactor. In the contactor, the lighter components of the feed are vaporized; asphaltenes and the high molecular weight compounds, which contain metals, sulfur and nitrogen contaminants, are deposited on the particles of the contact material. The metals invariably include vanadium and nickel. Some of the asphaltenes and high molecular weight compounds are thermally cracked to yield lighter compounds and coke. The metals that are present, as well as some of the sulfur and nitrogen bound in the unvaporized compounds, are retained on particles of contact material. At the exit of the contacting zone, the oil vapors are rapidly separated from the contact material and then immediately quenched to minimize incipient thermal cracking of the products. The particles of contact material, which now contain deposits of metals, sulfur, nitrogen, and carbonaceous material are transferred to the burner where combustible contaminants are oxidized and removed. Regenerated contact material, bearing metals but minimal coke, exits the burner and circulates to the contactor for further removal of contaminants from the chargestock.
In practice, the metals level of contact material in the system is controlled by the addition of fresh contact material and the withdrawal of spent contact material from the burning zone.
Generally, metals accumulated on the contact material used in the ART Process tend to be less active in forming coke than metals accumulated on cracking catalyst. Thus, the ART Process is able to operate effectively when accumulated metals are present on the contact material at levels higher than those which are generally tolerable in the operation of FCC units. For example, the process has operated effectively when combined nickel and vanadium content substantially exceeded 2% based on the weight of the calcined kaolin clay contact material.
The oxidation state of vanadium in the withdrawn particles will depend upon the conditions used in the burning zone. Typically, the vanadium is present in both V.sup.+5 and V.sup.+4 oxidation states even when the burner is operated with an excess of oxygen. A portion of the contact material with accumulated deposit may also be discharged with combustion gases and/or vaporized hydrocarbon product in the form of fines, i.e., particles not retained by cyclone separators in the contactor and/or burner zones.
In prior commercial practice, the spent contact material has been discarded without removing metals. It has been proposed to leach spent contact material to remove at least part of the metal contaminants before recycling the contact material to the system. This can result in a by-product solution containing nickel and vanadium. Under some conditions it may be desirable simply to dispose of the resulting leachate without recovering all of the metal values or without removing any metals.
Similarly, particles of spent fluid cracking catalysts will contain deposits of metal contaminants originating in the petroleum feedstock charged to the fluid catalytic cracking (FCC) unit. Spent catalyst particles are periodically withdrawn from the FCC regenerator in order to permit catalytic cracking units to operate at desirable activity and selectivity levels. See, for example, U.S. Pat. No. 4,268,188. The spent catalyst is frequently employed to start-up FCC units. Usually spent cracking catalyst particles, as well as fines discharged from FCC regenerators, are discarded and used as landfill. There has been a trend in recent years to charge FCC units with feedstocks which contain considerably higher levels of metal contaminants than the relatively "clean" gas oils heretofore used as FCC chargestock. Consequently, spent FCC catalysts may be expected to contain higher metals concentrations than were encountered in the past unless high catalyst replacement rates are used.
When discarded materials or leachates are to be disposed of as landfill, it is desirable to minimize leaching of water soluble heavy metals contaminants. Such materials are likely to come into prolonged contact with rain and/or surface waters, resulting in possible pollution of the waters. Generally, such waters are mildly acidic, e.g., the pH is about 3-5. Further, it is desirable to accomplish this result while minimizing treatment costs associated with chemical additives and equipment. Also, it is advantageous to provide material intended for disposal as landfill in the form of a solid or semi-solid mass amenable to direct disposal without a downstream filtration or dewatering step.
In addition to vanadium and nickel, metals originating in petroleum feedstocks may include one or more of the following as contaminants: chromium, cobalt, copper, arsenic, antimony, bismuth and barium. When present, these metals eventually form a deposit on spent cracking catalyst or spent contact material used in an ART unit. Constituents present in spent material that are leachable in water typically include V.sup.+5 and V.sup.+4 compounds. In some cases, nickel is also leachable. Generally, the leachates are mildly acidic, e.g., pH is 3 to 6. Thus, when such materials are disposed of as landfill, leaching of vanadium or vanadium and nickel is likely to occur. Processes capable of insolubilizing vanadium should also result in treated products in which leaching of the aforementioned other metals is minimal.
The difficulty involved in insolubilizing vanadium in spent contact material or cracking catalysts is that vanadium, an amphoteric element, is soluble at acidic pH values and is still somewhat soluble at neutral and mildly alkaline pH values at which other heavy metals such a nickel and iron are insoluble or are low in solubility. Vanadium compounds increase in solubility at strongly alkaline pH values.
Similar problems in insolubilizing vanadium while assuring limited solubility of other metals may be encountered in the disposal of vanadiferous solutions or slurries which contain vanadium in mixture with other heavy metals. Such solutions or slurries may result from treatment of used catalysts or contact materials or in disposing of ores, ore tailings or ore concentrates.
The present invention solves the problem of reducing the leachability of normally leachable vanadium compounds to minimum practical levels by addition of certain polyvalent ions which result in the conversion of the vanadium values of compounds that are insoluble at moderately acidic pH values, e.g., pH 5, at which other heavy metals are insoluble or substantially so.